1. Field of the Invention
The present invention relates to a radiation device, and particularly to a radiation device with a L-shaped ground plane.
2. Description of the Prior Art
In recent years, the communication industry has advanced vigorously and various communication products have been very successfully developed and manufactured. During this time, much attention has been paid to the design of the antenna of the related communication product. In the various antenna structures, the patch antenna is popular in the market for its characteristics of low profile and lower back radiation. However, the characteristic of the radiation pattern of the prior art patch antenna usually causes a maximum field is generated above the radiation patch in the direction perpendicular to the antenna (that is, θ=0° or having a broadside radiation pattern). And when the angle of |θ| increases, the radiation intensity of electric field will apparently increase. This kind of radiation characteristic for the antenna is unsuitable to the design of the radiation pattern needing omni-directional field above the radiation patch antenna. Although the variation of the filed of the antenna radiation pattern will slow down if the size of the ground plane is reduced, it will cost the gain of the antenna. Thus, the application of the prior art patch antenna is limited for the wireless communication product requiring an antenna with wider receiving/transmitting angle.
Please refer to FIG. 1. FIG. 1 is a perspective diagram of a prior art shorted microstrip antenna 10 with multiple ground planes. The antenna 10 comprises a radiation patch 11, a compound ground plane 11a, and a feeding-in device 15 for connecting the radiation patch 11 to the multiple ground planes 11a. The multiple ground plane 11a comprises a first grounding conductive sheet 12 parallel to the radiation patch 11, a second grounding conductive sheet 13 connected to the radiation patch 11 and the first grounding conductive sheet 12, and a third grounding conductive sheet 14. The third grounding conductive sheet 14 is perpendicular to the first grounding conductive sheet 12, and parallel to the second grounding conductive sheet 13.
The antenna 10 is so designed that the multiple ground planes 11a are employed for improving the beam-tilt characteristic caused by the shorted structure so as to promote the antenna gain in the z direction. Although the designed structure of the antenna 10 can improve the distribution of the radiation pattern, the multiple ground planes 11a have to be composed of three grounding conductive sheets 12, 13, 14 and the complexity of the structure design is increased. Besides, the second grounding conductive sheet 13 must be higher than the radiation patch 11, and the is will affect the appearance of the product and increase the cost.
Please refer FIG. 2. FIG. 2 is a perspective diagram of a coaxial line feed-in broadband patch antenna 20 having a U-shaped ground plane 22. The antenna 20 comprises an E-shaped radiation patch 21, a U-shaped ground plane 22, a coaxial feed-in line 23 for connecting the E-shaped radiation patch 21 and the U-shaped ground plane 22.
The antenna 20 is so designed that cross polarization of the radiation pattern is reduced so as to increase the purity of the linear polarization of the antenna. However, this designed structure will not apparently improve the gain of the antenna. In addition, as shown in FIG. 2, the U-shaped ground plane 22 has to have a planar ground plane 22a and two perpendicular ground planes 22b. In other words, the plane 22 is composed of three metal pieces so as to increase the complexity of the structure of the antenna 20.